The invention relates to an electromagnetic wave detector and, more particularly, an infrared radiation detector.
As is known, infrared detectors most often operate at low temperature, that is to say typically at temperatures of between 50 and 200 Kelvin. In fact, the detector device proper is generally associated with a cryostatic chamber (cryostat) which makes it possible, depending on the working temperature of the detector, to cool the latter by means of a cold finger supplied either with liquid helium or liquid air or liquid nitrogen, or else by a cryogenic source device.
The technical field of the invention will be discussed below with reference to FIG. 1 which represents an infrared detector of the prior art.
Heat exchange between the detector proper and the cryostat generally takes place via a cold finger (1) in direct contact with the cryogenic source, the end of this cold finger being hermetically sealed and having a cold plane (2) fixed in contact with it, which cold plane generally consists of a metal or ceramic part fixed to the cold finger by bonding or soldering.
In some cases, the cold plane (2) itself seals the cold finger (1). This cold plane is intended to accommodate the detection unit, that is to say the assembly consisting, on the one hand, of at least one electronic circuit (4) for detecting electromagnetic waves, which converts in known fashion electromagnetic radiation into an electrical signal and is associated with a read circuit (3) capable of converting the electrical signals output by the detection circuit (4), in particular by amplifying them to make them suitable for subsequent processing. The cold plane (2) additionally transfers heat between the cold finger (1) of the cryostat and said detection unit.
In most infrared detectors currently used, the detection circuit (4) is hybridized with the read circuit (3), for example by means of indium microbumps. Similarly, there may be a plurality of detection circuits on the same read circuit. In other applications, moreover, it is also possible to provide a plurality of read circuits and a plurality of detection circuits which are interconnected by hybridization via an electrical interconnection network underlying said detection and read circuits, the interconnection network including metallized contacts or tracks for providing electrical conduction between said circuits.
In most cases, the detection unit (3, 4) is mechanically fixed to a connection circuit (7) constituting a structure called the focal assembly, the connection circuit itself being constituted by a plate of an insulating material having, on its upper surface, that is to say the surface intended to come into contact with the detection unit, metal tracks and contacts (5) which also make it possible to solder the microwires (6). This connection circuit (7) has the function of transferring the electrical signals from the read circuit (3) to the internal connection system proper of the cryostat, which system is itself connected to a connector consisting, in known fashion, of a part making it possible to transfer the electrical signals out of the cryostat, while sealing off the internal part of the latter from the outside. There are many well-known techniques for fabricating these connectors, and these are described, for example, in documents DE-A-3,344,713 and U.S. Pat. No. 3,259,865.
In view of the interconnection method, in particular between the detection unit (3, 4) or the focal assembly (3, 4, 7) and the connector, a cryostat whose geometry depends directly on the geometry of the component which constitutes it, is associated with each type of detector.
More specifically, the connector of the cryostat, the function of which is to transfer the electrical signals out of the cryostat without breaking the seal of the latter, and additionally making it possible to analyze the electrical signals outside the cryostat, in particular by means of pins, has dimensions and a configuration (number and positioning of the pins, etc.) which are directly linked with those of the detector. In fact, producing specific connectors for each of the detector types employed gives rise to a significant cost increase and nonnegligible time losses.
It has therefore been deemed desirable to standardize, and in any case to regularize, the dimensions of the connector independently of the geometry of the detector employed, and therefore to standardize the connector/cryostat electrical interfaces. In other words, for a fixed connector geometry, it is desired to make it possible to associate all types of constituent component of the detection unit or of the focal assembly, of variable dimensions and, in particular, detectors with large dimensions, and additionally to make it possible to produce the electrical connections between the detector and the connector easily.
Connecting the detection unit (3, 4) or the focal assembly (3, 4, 7) to the internal connection system of the cryostat often requires the use of flexible lines such as electrical conductors which are difficult to use and have the critical drawback of giving rise to vacuum degassing phenomena which are significant and are therefore capable of detrimentally affecting the working life without maintenance. In addition, such flexible lines have, after they are fitted, offsets which are also significant and can hinder the fixing of a heat and/or optical screen whose function may prove essential in the context of optimizing the measurements and detections made with such a device.